Antiknock motor fuels



United States Patent 3,113,855 ANTlKblQCK MGTQR FUELS Anthony F. Banning, Woodstown, N..l., assignor to E. i. du Pont de Nemeurs and ornpany, Wilmington, Deb, a corporation of Belawarc No Drawing. Filed Mar. 18, 196%, Ser. No. 15,849 12 Claims. (3. a i -6i) This invention relates to antiknoclr motor fuels and more particularly to motor fuels for internal combustion engines which motor fuels comprise hydrocarbons in the gasoline boiling range that contain lithium salts of certain substituted carboxylic acids as antilrnocl: agents.

The development of internal combustion engines of high compression ratios has established a need for high quality fuels having increased resistance to knock over a wide range of engine operating conditions. Careful refining and blending of fuel components can produce a fuel of sufficiently increased knock resistance to satisfy the engine requirements under the previously mentioned conditions, but such fuels are diilicult and costly to produce. Usually, tetraethyllead is today employed in these fuel blends to provide the knock resistance which can not easily and economically be obtained through refining techniques. Tetraethyllead is widely used since it does impart improved antilcnock quality over the wire range of engine conditions mentioned above. The use of tetraethyllead, however, has limitations. Each successive increment of tetraethyllead produces only a fraction of the improvement in antiknock rating obtained with each previous increment.

Heretofore it has been proposed to employ in motor fuels for various purposes a variety of organometallic compounds, including some organic lithium compounds (other than those of the present invention). For example, Taveau in US. Patent 1,991,127 has proposed to employ lithium alkyls and lithium aryls in motor fuels of low antiknock value. However, such lithium compounds are quite unstable and tend to decompose in the presence of moisture, air or gases such as carbon dioxide, and furthermore have little or no appreciable antiknock effect when employed in internal combustion engines. At an even earlier date, British Patent 300,156, it was proposed to employ lithium oleate and lithium naphthenate as antiknock agents in straight-run gasolines having an octane number of a low order (about 50). However, lithium oleate has but little antiknock effect. Lithium naphthenate also has but little antiknock effect in motor fuels of the type disclosed, having a low octane value. Other organometallic compounds, including some lithium compounds, have been proposed for use as anti-preignitiou compounds, but they require a deposit on the piston top and cylinder head in order to so function, and are not antiknock agents.

It is an object of the present invention to provide motor fuels containing new and improved antiknock compounds for internal combustion engines. Another object is to provide motor fuels of such character which function over a wide range of engine operating conditions. A further object is to provide new and improved antiknoclr compounds for fuels which contain tetraethyllead, which new antiknocl; compounds increase the knock resistance of the fuel to an extent which is not attainable by the use of tetraethyllead alone. A still further obg'ect is to provide novel antilcnock compounds which are superior to tetraethyllead under severe operating conditions such as are normally encountered in aircraft or in high compression automotive engines. Other objects are to provide new In compositions of matter and to advance the art. other objects will appear hereinafter.

The above and other objects may be accomplished in accordance with the present invention wherein there is provided a motor fuel for internal combustion engines which fuel comprises hydrocarbons boiling in the gasoline boiling range containing, in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of the formula Li0OC-Q-OR wherein R is an alkyl radical of l to 15 carbon atoms and Q is a hydrocarbon radical of 1 to 6 carbon atoms. A particular feature of this invention involves the provision of motor fuels of the above character which, in addition to the lithium compounds, contain tetraethyllead.

it has been found that the lithium compounds of this invention are very effective to increase the antiknock properties of motor fuels of varying types in the absence and in the presence of tetraethyllead. They are effective over a Wide range of engine operating conditions. In the presence of *tetraethyllead, they increase the antilillOCl-I properties of the fuel to a much greater extent than can be obtained by corresponding increases in the amount of tetraethyllead.

The present invention is particularly applicable to hydrocarbon fuels for internal combustion engines and more particularly to fuels which may be a mixture of Still hydrocarbons boiling in the gasoline range, or a refined gasoline as defined in the ASTM D28853 (adopted 1939, revised 1953). Such fuels may be clear fuels or fuels containing organ c-lead antikn ocl; compounds such as tetraalkyl'leads. Such organodead compounds may be used in amounts up to the equivalent of 6 ml. of tetraethyllead per gallon of fuel. V/hen used, the organo-lead compound usually will be tetraethyllead and usually will be present in an amount less than 4 ml. per gallon of fuel. in place of the tetraethyllead, tetrarnethylle-ad may be used. Also, the fuels may be finished fuels which contain varying amounts of conventional fuel additives such as scavenging agents, dyes, antioxidants, anti-i Zng agents, rust inhibitors, corrosion inhibitors, inhibitors of haze formation, inhibitors of gum formation, anti-preignition agents, and the like.

The lithium compounds which are employed in accordance with this invention are the lithium salts having the formula LiOOC-Q-OR wherein R is an alkyl radical of 1 to 15 carbon atoms, preferably 1 to 4 carbon atoms, and Q is a hydrocarbon radical of l to 6 carbon atoms. The alkyl radical, R, may be straight-chain or branchedchain. The radical Q may be an acyclic radical, including straight-chain or branched-chain, or an alicyclic radical which may contain an alkyl side chain. It will be understood that an acyclic radical is an open-chain radical, and an alicyclic radical means a saturated cyclic hydrocarbon radical. A. preferred class of compounds consists of the lithium salts of the monoalkoxy substituted alkanemonocarboxylic acids of 2 to 7 carbon atoms; i.e.,. wherein Q is a saturated acyclic hydrocarbon radical of l to 6 carbon atoms. Particularly preferred compounds are the salts of the alkoxy-substituted propionic and butyric acids (Q has 2 to 3 carbon atoms), especially the alkoxy-substituted isobutyric acid. Also, preferably, the alkoxy (RO) group is atached to a carbon atom which is in one of the positions 2, 3 or 4 of the alkanecarboxylic acid nucleus.

Representative lithium salts of this invention are lithium isopropoxyacetate, lithium Z-isopropoxyisobutyrate, lithium 3-methoxypropionate, lithium 2-methyl-3-methoxypropionate, lithium S-butoxypropionate, lithium Z-methoxyisobutyrate, lithium 1-methoxycyclohexanecarboxylate,

3 lithium 3-ethoxypropionate, lithium Z-methoxybutyrate, lithium 4-rnethoxy-2-nethylbutyrate, linhium 2-ethoxyisobutyrate, lithium 2-decoxyisobutyrate, lithium 2-dodecoxypropionate, and lithium 2-pentadeco yisobutyrate. Lithium 2-isopropoxyisobutyrate is preferred.

The lithium salts of this invention are readily prepared by the reaction of the appropriate acid with a lithium base, preferably lithium hydroxide monohydrate. Lithium metal, lithium hydride,lithium alkoxide or lithium carbonate may also be used to advantage to form the lithium salt. The salts are readily obtained by neutralizing the acid with a stoichiometric quantity of the lithium base followed by recovery of the saft from the solution. For ease of isolation in pure form, the salt is best prepared in an inert organic solvent, such as benzene, toluene, ether and dioxane. In general, the carboxylic acids and their anhydrides, and the methods of preparing them are known to those skilled in the art.

These compounds are effective irrespective of the meth- .od by which they are introduced into the cylinder of the engine. While they are normally introduced with the fuel itself, they may be introduced separately as a dust or powder, or with solvents (used either to carry them alone or in the supplementary antiknock solutions such as the water/ alcohol mixture employed in aircraft engines or the tetraethyllead/ alcohol mixtures employed in automotive engines).

The amount of the lithium compound usually employed will vary with the quality and intended use of the fuel. Normally, the amount employed will depend upon the molecular weight of the compound, but should be such as to give 0.01 gram to about 2.0 grams of lithium metal per gallon of the fuel, regardless of the presence, or the amount of tetraethyllead in the'fuel. Single members of the class of the lithium salts of this invention or mixtures of any two or more members thereof may be used as desired.

Blending agents may be employed to enhance the solubility of the lithium antiknock compounds of this invention in the fuel. Typical blending agents are gasoline miscible glycols, esters, ketones, amides, alcohols, and other polar organic liquids. Methanol, ethanol and isopropanol are particularly suitable blending agents. The lithium compounds may be dissolved directly in the blended motor fuel or added as a concentrated solution in the blending agent.

In the examples given hereinafter, three knock test methods were employed which are representative of automotive and aircraft operating conditions. One of these tests is a fuel injection test, a second is a carburetion engine test, and the third represents supercharged aviation conditions. In the fuel injection test, the fuel samples were tested in a Waukesha ASTM D909-49T Knock Test Method single cylinder knock rating engine equipped with a four-hole, overhead valve, variable compression ratio head. The engine is mounted on a test stand with a suitable motor-generator unit which absorbs the power output of the engine. 'A spark plug, mounted in the conventional position for this type engine, a rate of change of pressure pick-up and a steel plug occupy three of the four holes in the head. A Waukesha ASTM D-909-49T Knock Test Method fuel injector is inserted into the fourth hole in the head by means of an adapter, and is supplied with fuel from the fuel injection pump. This fuel system injects the fuel directly into the combustion chamber. With the engine operating, the occurrence of knock is determined at the trace knock intensity level by means of'the rate of change of pressure pick-up mounted in the cylinder head. The signal from the pick-up feeds into a cathode-ray oscilloscope, and the occurrence of knock is observed as a shattering of the rate of change of pressure trace on the oscilloscope screen late in the engine cycle.

h 11 rasse The engine is operated under the following conditions:

Speed, r.p.m 600. Spark advance (degree before top center) 13. Fuel injection timing (degree after top center on intake stroke) 5-0. Fuel/air ratio 0.0800i0.0(l05. Intake manifold air pressure, (in.

Hg abs.) 30. Coolant temperature, F. 212. Intake air temperature, F 200. Oil temperature, F 160. Compression ratio Varied to produce trace knock.

These tests and the test conditions were developed to evaluate antiknock compounds under stresses encountered in automotive operation.

Under these operating conditions, the knock resistance of all fuels tested is determined by comparing the highest usable knock-free compression ratio of these fuels to that of primary reference fuels consisting of blends of isooctane and n-heptane below performance number, and isooctane plus tetraethylled above 100 performance number. The knock resistance of all fuels tested is expressed in terms of Army-Navy Performance Numbers'as defined in Tables VII and VIII in the ASTM Aviation Method (D614-49T), as recorded in the ASTM Manual of Engine Test Methods for Rating Fuels, published by the American Society for Testing Materials, October 1952.

In the carburetion engine test (ASTM 13-357), the fuel was metered to the combustion chamber of the engine through the carburetor and the intake manifold, and the compression ratio to obtain standard knock intensity was measured.

The supercharged aviation tests were carried out in an engine equipped for manifold fuel injection in accordance with the procedure set forth in ASTM D-909-49T.

The following examples are given to more clearly illustrate this invention, preferred modes of carrying it into effect and the advantageous results obtained thereby wherein the percentages employed are by volume except where specifically indicated otherwise.

Example 1 To a blend of hydrocarbons comprising by volume 30% 'olefinic hydrocarbons, 34% saturated hydrocarbons, and 36% aromatic hydrocarbons and simulating a gasoline stock, was added 3 ml. of tetraethyllead per gallon and two volume percent of absolute ethanol as a solubilizing agent to make a fuel blend having a performance number of in the fuel injection test. To this fuel blend was added lithium 2-isopropoxyisobutyrate to give 0.25 gram of lithium per gallon. As a result, the performance number of the fuel blend in the test was increased to 118.

In a similar way other alkoxy substituted lithium carboxylates were tested using the same fuel blend containing 3 ml. of tetraethyllead per gallon but different amounts of ethanol under the same test conditions with the following improvements in antiknock properties of the fuel:

When methyl lithium and tert.-butyl lithium were tested under the same test conditions, they showed no antiknock activity. When tested under the same test conditions with and Without added tetraethyllead, lithium oleate and lithium naphthenate showed only a slight increase in performance number, considerably less than the compounds of this invention.

Example 2 To the blend of hydrocarbons of Example 1 was added 2-volume percent of ethanol, 3.0 ml. of tetraethyllead per gallon and lithium 2-isopropoxyisobutyrate to provide 0.25 g. of lithium metal per gallon of fuel. The fuel Was metered through the carburetor and intake manifold of a standard carburetion engine as set forth in ASTM D-359 procedure, and the compression ratio to obtain a standard knock intensity was measured. When the engine was operated on the base fuel alone without the lithium additive, the compression ratio required to reach a standard knock intensity was 6.50 to 1. With the lithium compound in the fuel and after an induction period of about 5 minutes, a substantial antiknock effect was manifest and the engine could not be made to knock even when the compression ratio was increased to 10.0 to l, the limit of the engine. The antiknock elfect exceeded that which corresponds to an increase in the compression ratio from 6.5 to 1 to a ratio of 10.0- to 1. This is equivalent to an increase in the antiknock performance number of over 80.

Example 3 Lithium Units Concn., Ethanol, Increase Lithium Salt glgal. Vol. in Peruel Percent formance Number (a) Lithium 2-ethoxyisobutyrate g: g 0. 044 0 44 (b) Lithium 2-decoxyiso-butyrate 0. 15 0 49 1 Over that of the base fuel or over that of the base fuel plus alcohol.

The definite antiknock effect of the lithium compounds is indicated by the substantial increase in performance number.

The lithium salts of polyalkoxyalkanoic acids, such as lithium 3 methoxy-2,2-bis(methoxymethyl)propionate for example, may be used as antiknock agents to obtain similar results.

It Will be understood that the preceding exarnples have been given for illustrative purposes solely and that this invention is not restricted to the specific embodiments described therein. On the other hand, it will be apparent to those skilled in the art that, subject to the limitations set forth in the general description, the materials, proportions, conditions and techniques employed may be widely varied without departing from the spirit or scope of this invention.

From the preceding description, it will be apparent that this invention provides motor fuels for use in internal combustion engines, which fuels contain newand improved antiknock compounds that function over a wide range of engine operating conditions and very materially increase the antiknock properties of the fuels. Under severe operating conditions and in the presence of tetraethyllead the new antiknock agents are superior to tetraethyllead. Therefore, it is believed that this invention constitutes a valuable advance in and contribution to the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A hydrocarbon fuel for internal combustion engines boiling in the gasoline boiling range which cont ains, in an amount suificient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkoxy substituted alkanemonocarboxylic acid of 2 to 7 carbon atoms in which the alkoxy group contains 1 to 15 carbon atoms.

2. A hydro-carbon fuel for internal combustion engines boiling in the gasoline boiling range which contains, in an amount suflicient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkoxy substituted alkanemonocarboxylic acid of 2 to 7 carbon atoms in which the alkoxy group contains 1 to 15 atoms and is attached to a carbon in one of the posit-ions 2 to 4 of the alkanecarboxylic acid nucleus.

3. A hydrocarbon fuel for internal combustion engines boiling in the gasoline boiling range which contains, in an amount sufiicient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of 1a monoalkoxy substituted alkanemonocarboXyl-ic acid of 2 to 7 carbon atoms in which the alkoxy group contains 1 to 4 carbon atoms.

4. A hydrocarbon fuel for internal combustion engines boiling in the gasoline boiling range which contains, in an amount sufficient to provide from about 0.01 to about 2.0 gramsof lithium metal per gallon of fuel, at least one lithium salt of a monoalkoxy substituted isobutyric acid in which the alkoxy group contains 1 to 4 carbon atoms.

5. A hydrocarbon fuel for internal combustion engines boiling in the gasoline boiling range which contains, in an amount suificient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, lithium 2-isopropoxyisobutyrate.

6. A hydrocarbon fuel for internal combustion engines boiling in the gasoline boiling range which contains up to 6 ml. of tetraethyllead per gallon of fuel and, in amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkoxy substituted alkanemonocarboxylic acid of 2 to 7 carbon atoms in which the alkoxy group contains 1 to 15 carbon atoms.

7. A hydrocarbon fuel for internal combustion engines boiling in the gasoline boiling range which contains up to 6 ml. of tetraethyllead per gallon of fuel and, in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkoxy substituted alkanemonocarboxylic acid of 2 to 7 carbon atoms in which the alkoxy group contains 1 to 4 carbon atoms.

8. A hydrocarbon fuel for internal combustion engines boiling in the gasoline boiling range which contains up to 6 ml. of tetraethyllead per gallon of fuel and, in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkoxy substituted alkanemonocarboxylic acid of 2 :to 7 carbon atoms in which the allcoxy group contains 1 to 4 carbon atoms and is attached to a carbon in one of the positions 2 to 4 of the alkanecarboxylic acid nucleus.

9. A hydrocarbon fuel for internal combustion engines boiling in the gasoline boiling range which contains up to 6 m1. of tetnaethyllead per gallon of fuel and, in an amount suflicient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of a monoalkoxy substituted isobutyric acid in which the alkoxy group contains 1 to 4 carbon atoms.

10. A hydrocarbon fuel for internal combustion engines boiling in the gasoline boiling range which contains up to 6 m1. of tetraethyllead per gallon of fuel and,

in an amount sufficient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, lithium 2-isopropoxyisobutyraltc.

11. A hydrocarbon fuel for internal combustion engines boiling in the gasoline boiling range which contains, in an amount suflicient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of an ailkoxy substituted monocarboxylic acid wherein each alkoxy group contains from 1-15 carbon atoms and wherein the 'alkoxy groups and the calrboxylate radical are attached ltO' a hydrocarbon radical of 1 to 6 carbon atoms which is a member of the group consisting of acyclic and alicyclic radicals.

12. A hydrocarbon fuel for internal combustion engines boiling in the gasoline boiling range which contains up to '6 ml. of tetraethyllead per gallon of fuel and, in an amount sufiicient to provide from about 0.01 to about 2.0 grams of lithium metal per gallon of fuel, at least one lithium salt of an alkoxy substituted mono carboxylic acid wherein each alkoxy group contains from E a 1-15 carbon atoms and wherein the alkoxy groups and the carboxylate radical are attached to a hydrocarbon radical of 1 to 6 carbon atoms which is a member of the group consisting of acyclic and al-icyclic radicals.

References Cited in the file of this patent UNITED STATES PATENTS 1,991,127 'I aveau Feb. 12, 1935 2,728,648 Hirschler et al. Dec. 27, 1955 2,935,973 Sandy et al. May 10, 1960 2,935,974 Sandy et a1 May 10, 1960 2,935,975 Sandy et a1. May 10, 1960 FORETGN PATENTS 300,156 Great Britain Nov. 6, 1928 72 Trinidad and Tobago "Oct. 9, 1958 OTHER REFERENCES Texaco, Abstract of Australian Patent 42,139, October 8, 1958. 

1. A HYDROCARBON FUEL FOR INTERNAL COMBUSTION ENGINES BOILING IN THE GASOLINE BOILING RANGE WHICH CONTAINS, IN AN AMOUNT SUFFICIENT TO PROVIDE FROM ABOUT 0.01 TO ABOUT 2.0 GRAMS OF LITHIUM METAL PER GALLON OF FUEL, AT LEAST ONE LITHIUM SALT OF A MONOALKOXY SUBSTITUTED ALKANEMONOCARBOXYLIC ACID OF 2 TO 7 CARBON ATOMS IN WHICH THE ALKOXY GROUP CONTAINS 1 TO 15 CARBON ATOMS. 